In automated medical specimen diagnostic instruments (clinical analyzers and immunoassay instruments), patient biological specimens as well as reagents, acids, and bases may be dispensed. Some immunoassay systems may use a simple pressure measurement technique to verify a proper aspiration of the patient biological specimen. However, existing production immunoassay systems simply rely on the general reliability of the liquid delivery system to ensure integrity of acid and base additions. If there are small air bubbles in the liquid delivery line for the acid or base, this may not be detected.
Some existing systems utilize a capacitance sensing technique to confirm the liquid depth of the patient biological specimen, reagent, or combination of specimen and reagent. This capacitive probe technique requires a moving conductive probe, which touches a surface of the specimen, reagent, or combination. However, capacitance sensing is difficult, due to the possible existence of foaming on top of the liquid.
Accordingly, diagnostic instruments having improved ability to effectively verify liquid delivery are desired.